Circuit for operating multiple position display tubes

ABSTRACT

The disclosed apparatus is adapted for operating multiple position display devices having several groups of display cathode segments or elements, with corresponding elements electrically interconnected, an anode associated with each group of segments, and an auxiliary electrode common to all of the groups of electrodes for electrically isolating the electrode groups and preventing spurious glow between them. The subject circuits include a common impedance or a voltage divider connected to both the auxiliary electrode and the cathode drivers to bias the auxiliary electrode proportional to a reference potential and to vary the common impedance inversely proportional to the number of cathode segments being energized, for inhibiting electrical discharge between the cathode segments and any other than the associated anode. Apparatus is also provided for biasing the OFF cathodes and the OFF anodes in a non-conductive state when not energized.

United States Patent Harv [ Dec. 11, 1973 Primary ExaminerRudolph V.Rolinec Assistant Examiner-Marvin Nussbaum Attrney-George L. Kensingeret al.

[75] Inventor: Edgar Lloyd Harvey, Old Bridge,

N.J. [57] ABSTRACT [73] Asslgnee: ai L Corporatmn Detrolt The disclosedapparatus is adapted for operating mul- 1c tiple position displaydevices having several groups of [22] Filed: Jan. 16, 1973 displaycathode segments or elements, with corresponding elements electricallyinterconnected, an [211 App! 324023 anode associated with each group ofsegments, and an Related US. Application Data auxiliary electrode commonto all of the groups of [63] Continuation of 126,325 March 22 1971electrodes for electrically isolating the electrode abandonei groups andpreventing spurious glow between them. The subject circuits include acommon impedance or [52] S. Cl 315/169 R, 315/334, 3l5/336, a voltagedivider connected to both the auxiliary elec- 315/169 TV trode and thecathode drivers to bias the auxiliary 51 Cl 013 17 4 051 37 00 41 00electrode proportional to a reference potential and to [58] Field ofSearch 315/167, 168, 169 R, y the common impedance inverselyproportional to 315/169 TV, 334, 336; 313/1095 the number of cathodesegments being energized, for inhibiting electrical discharge betweenthe cathode [56] R f n Ci d segments and any other than the associatedanode.

UNlTED STATES PATENTS Apparatus is also provided for biasing the OFFcathodes and the OFF anodes in a non-conductive. state 2,906,906 9/1959McCauley et al 313/1095 when not ener ized 3,509,420 4/l970 Ogle 315/169R g 21 Claims, 3 Drawing Figures ragga 210 I SEQUENCER l4 "24H #251 29 I212% 0 H0O i :I A 255 295 T 250 I 290 id A I32 S m 245 2|5 e R L- 34 -3539 I20 E 133 r W 23 7 V 7 V 230 /7-\ i I40 ,4! 150 5! I 9 21, 04 V U oI34 115 22 A A 25 x5 55 e imo PMENIEDnEc 1 1 I975 SHEET 2 0F 2 EDGAR L.HARVEY mwUZm30mm OOT ATTORNEY CIRCUIT FOR OPERATING MULTIPLE POSITIONDISPLAY TUBES This patent application is a continuation of applicationSer. No. 126,825, filed Mar. 22, 1971, now abandoned.

BACKGROUND OF THE INVENTION The invention relates to circuitry foroperating multiple position gas discharge devices such as display panelshaving a plurality of interconnected cathode elements positioned in arow. More particularly, the invention relates to the operation ofmultiple position gas discharge devices having a plurality of segmentedcathode electrodes for displaying characters side-by-side.

A multiple position display device which is available commercially isknown as the PANAPLEX numeric panel display. This type of display panelincludes a plurality of groups of display cathode elements in the formof elongated bars or segments. Each group of segments is arrayed in afigure 8 pattern or the like and the various segments, together with ananode, can be selectively energized to display a character at anydesired cathode group or position by discharge in the gas about theelectrodes. The electrical discharge results in cathode glow on theselectively energized segments which displays the desired character.

One such display panel includes an auxiliary electrode common to all theelectrode groups which is biased intermediate the cathode and anodepotentials for preventing spurious electrical discharges and theresultant spurious glow among the electrodes, as described and claimedin Harvey et al, S.N. 78,045, filed Oct. 5, 1970 now abandoned. Theauxiliary electrode, however, receives a current from ionization in thedevice which tends to raise its potential in proportion to the number ofcathode segments being energized and this reduces its effectiveness. Atthe same time, the initial bias on the auxiliary electrode cannot bereduced enough to offset completely this rise in potential when cathodesegments are selected since the auxiliary electrode then tends todevelop cathode glow itself.

Two recently developed circuits for operating such display panels aredisclosed and claimed in G. E. Holz, et al, SN. 85,662, filed on Oct.30, 1970 and in G. E. Holz, S.N. 87,058, filed on Nov. 5, 1970 now Pat.No. 3,694,693, issued Sept. 26, 1972. Those circuits, while suitable foroperating many panels under certain conditions of operation, are limitedin flexibility and introduce undesired costs or complexity to such paneldisplays.

SUMMARY OF THE INVENTION Accordingly, an object of this invention is toimprove spurious glow suppression in multiple position display deviceshaving interconnected cathode elements or segments.

Another object of the invention is to simplify and reduce the cost ofsuch multiple position panel displays having auxiliary electrodes forspurious glow suppres sion.

In accordance with these objects, a circuit of the invention includescommon impedance or voltage dividing means coupled between first andsecond reference terminals for the display device and having a junctionto which is connected the auxiliary glow suppression electrode of amultiple position display panel, together with the output of each of thecathode drivers including second impedance means. The bias potentialapplied to the auxiliary electrode for suppressing spurious glow isthereby maintained proportional to the supply potential on the device.The effective biasing impedance is changed in inverse proportion to thenumber of cathode segments being energized since the cathode drivers,when activated, are in electrical parallel with the common impedance,draw current from the voltage dividing means, and reduce the potentialon its junction. The circuit also includes means for biasing the OFFcathodes and the OFF anodes in a non-conductive state when notenergized.

DESCRIPTION OF THE DRAWINGS Other objects and features of the subjectinvention will become clear from the following detailed descriptionwherein:

FIG. I is an isometric view of a segmented-cathode display tube havingindividual anodes and an overlying auxiliary electrode;

FIG. 2 is an elevational view of a longitudinal section of the displaytube or panel of FIG. I; and

FIG. 3 is an electrical schematic diagram of a preferred embodiment ofthe circuit of applicants invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principles of the inventionare particularly applicable to operation of the type of display deviceor panel described and claimed in the above-identified Harvey, et al.patent application. Some of the features of such a device as shown inFIGS. l and 2 for a display panel or tube 10 having three representativedisplay positions. A plurality of groups of cathode segments 41-47,51-57, and 61-67 are connected to corresponding conductors 2l.-27 whichare spaced from each other on an insulating base plate 20 or withingrooves in its surface as shown in FIG. 2. Ari anode electrode 140, 150,160, is provided for each group of segments. An insulating sheet orlayer 30 shields cathode conductors 21-27 from the anodes, as shown inFIG. 2, to prevent them from glowing.

The anodes in FIG. 1 are each shown as a ring surrounding the associatedgrottps of cathodes, but they may be screen electrodes situated abovethe associated cathode groups, or they may take any other desired shape.In addition, the device includes an auxiliary screen electrode 230disposed above the groups of cathodes and anodes and electricallyassociated with all of the electrode groups. Top and bottom insulatingplates 200 and 20, respectively, sealed together by a glass or ceramicfrit 15 or the like, complete the panel or tube structure.

Briefly, in operation of the panel or tube shown in FIGS. 1 and 2, drivesignals are applied to the cathodes via conductors 21-27 in accordancewith the input information. Simultaneously, the anodes are energized inturn from left to right, or in any other desired order or sequence vialeads 34, 35, 36 in synchronism with the cathode drive signals, to causethe cathode segments in the selected groups to glow. A suitable biaspotential intermediate the cathode and anode bias potentials is appliedto lead 235 of screen electrode 230 for preventing spurious glow aboutthe cathode segments and between adjacent display positions. The biasedauxili ary electrode prevents extraneous discharges from occurringbetween an energized anode and the cathodes in adjacent groups whichhave operating potential applied to them.

A preferred embodiment of the invention is illustrated in FIG. 3 inwhich display device 19 is shown schematically. Display segments All,51, 91 are connected to cathode conductor 21 which is driven from thecollector of NPN transistor 121. Likewise, cathode segments 42-92,13-93, 44-5 4 and 65-95 are connected to the collectors of cathodedrivers 122, 123, 124 and 125 by conductors 22, 23, 2d and 25,respectively Cathode conductors 21-25 are also coupled to the cathode ofZener diode 118 at circuit junction by resistors 131-135, respectively.The anode of Zener diode 118 is connected to B reference terminal 120and resistor 14 couples circuit junction 15 to E reference terminal 12.

A voltage divider comprising resistors 13 and 19 is connected betweenanode bias terminal 12 and cathode bias terminal 121). The collectors ofcathode driver transistors 121-125 are coupled to voltage dividerjunction 16 by resistors 111-115 connected in series with diodes101-105, respectively. The cathodes are initially biased OFF by thevoltage on circuit junction 15. The difference in potential between theOFF cathodes and the ON anodes must not exceed the ionization voltage inthe panel.

The base electrodes of the cathode driver transistors 121-125 areconnected to data source 100 for receiving positive-going informationsignals and they either limit cathode current in the device whenoperated or are connected to suitable current-limiting impedances. Datasource 100 may include a computer and associated elements, a charactergenerator or suitable decoders and encoders for providing informationsignals to the cathode drivers.

Anode leads 34-39 of anodes 140, 151 190 are connected to the outputs ofanode drivers 240, 251), 290 and to the cathodes of diodes 245, 255,295, the anodes of which are connected to the cathode of Zener diode 218at its junction 215 with resistor 212. The input terminals 241, 251, 291of the anode drivers are connected to a suitable sequencing circuit ordevice 210 for receiving anode control signals. The anode drivers 240,250, 290 are referenced to E potential terminal 12, as shown, and applya suitable positive potential to each anode in turn under control of thesequencer.

The anode electrodes 1411-1911 are initially biased OFF through diodes2&5, 255, 295 by the voltage across Zener diode 218, connected in serieswith resistor 212 between the voltage supply terminals 12 and 120. Thepotential difference between the OFF anodes and the ON cathodes is lessthan the ionization voltage for the device,

The display panel or tube 11 is operated in the multiplex mode.information signals are applied to cathode drivers 121-125 from datasource 100 and, at the same time, operating potential is applied to theanodes in turn. As each anode is energized, the appropriate informationsignals are applied to the cathodes so that the desired information isdisplayed at each position.

Auxiliary electrode 230 is usually biased at a potential intermediatethe anode and the cathode bias potentials from a voltage source havingappreciable internal impedance or other impedance connected betweenthem. During operation, auxiliary electrode 231) then conducts a leakagecurrent from whichever anode Mid-1%) is energized, into the associatedvoltage source or impedance device. This raises the potential on theauxiliary electrode as more cathode segments are energized or as thecathode current is increased. This rise in the potential on theauxiliary electrode toward the anode potential reduces the effectivenessof the auxiliary electrode in suppressing spurious glow in the device.

in the present embodiment, electrode lead 235 of auxiliary electrode2311 is connected to junction 16 of the common voltage divider resistors13 and 19, as are the collectors of cathode driver transistors 121-125,through resistors 111-115 and diodes 1111-1115. The voltage divider is,therefore, connected in common to the auxiliary electrode and to theoutput terminals of the cathode drivers. Since the emitters of cathodedrivers 121-125 and resistor 19 of the voltage divider are all connectedto E reference terminal 121), the resistors 111-115 in the drivercollector circuits effectively appear in parallel to resistor 19 whenthe drivers are operated and reduce the effective biasing resistance forauxiliary electrode 2311 accordingly.

Since all of the cathodes are connected to circuit junction 16 of thevoltage divider, current is conducted from voltage divider resistor 13by the actuated ones of cathode drivers 121-125. These currents inresistor 13 tend to drop the potential on the auxiliary electrode inopposition to the potential rise caused by the abovementioned leakagecurrent conducted by it from the actuated electrode. By proper selectionof the values of voltage divider resistors 13 and 19 and by-pass orcoupling resistors 111-115, the opposing changes in potential onauxiliary electrode 230 may be made to counteract each other, withoutsignificantly affecting the glow inhibiting potential on the auxiliaryelectrode. The auxiliary electrode is thus held at or near the optimumpotential for spurious glow suppression regardless of how many cathodesare energized or the particular pattern being displayed.

The incorporation of diodes 1111-1115 between the cathode drivertransistors and the common voltage divider is made necessary by thedirect biasing of the OFF cathodes to the E reference potential terminal12 through resistors 1d and 131-135. Diodes 1111- prevent the OFFcathode bias potential on cathode conductors 121-125 from affecting thepotential on junction 16 of the voltage divider and, consequently, theglow inhibiting potential applied to auxiliary electrode 231).

in operation of panel 1% to display a plurality of numerals, negativeinformation signals are applied to one or more cathode conductors 21-27from a suitable data source 1110, and a relatively positive potentialmay be applied to the first anode 1 m. The selected ones of cathodesegments 41-47 which are thus energized, will glow and display a numeralat the first display position. A second group of information signals isapplied to selected ones of cathode conductors 21-27 and the secondanode 150, for example, is energized. The second numeral is displayed bythe selected cathode segments 51-57 at the second display position. inthe same way, the successive application of different informationsignals to selected cathode conductors and to the anodes, in turn,causes a character to be displayed at each character position. if thissequence is repeated through the display device from one end to theother at a sufficiently high rate, a stationary, but changeable, seriesof numerals can be displayed in the panel, one at each characterposition, if desired. As the cycling operation is carried out, thecharacters at the respective display positions change if the informationsignals on the cathode conductors change.

The above-described mode of operation utilizes sequential time-shareddriving of anode electrodes 140, 150, 160, etc. of the device. Thissequentially energizes the successive display positions along thedevice. Another mode of operation involves time-shared driving of thecathode electrode segments. In this mode, the anodes 140, 150, 160, etc.are selectively energized from a data source, for example, and cathodeconductors 21-27 are energized successively for sequencing the display.The energization of anode electrodes 140, 150, 160, etc. is changed asdesired for varying the pattern of the display. The anodes and cathodesmay be energized in any other desired order or sequence, also, dependingupon the desired mode of display.

Although the preferred embodiment of the invention has been described indetail, it should be understood that the present disclosure has been byway of example only. Many modifications and variations of the inventionare possible in light of the above teachings. it is, therefore, to beunderstood that the invention may be practiced otherwise than asspecifically disclosed.

What is claimed is: 1. Apparatus for operating multiple-position displaydevices having a plurality of interconnected groups of cathode elements,an anode associated with each of the groups and an auxiliary electrodethat is common to all of the groups and shields them from each othercomprising a plurality of drivers having their output terminals coupledto corresponding ones of the interconnected cathode elements forenergizing them selectively in response to a first set of input signals,

voltage dividing means coupled between a pair of reference terminals andhaving a divider junction,

means coupled to each of the anodes for energizing them selectively inresponse to a second set of input signals, and being biased in commonwith the voltage dividing means from one of said reference terminals,

the auxiliary electrode being coupled to the divider junction to bebiased at a level that is directly proportional to the anode biasingpotential for preventing spurious glow in the device irrespective ofvariations in the bias potential available for the device.

2. The apparatus for operating multiple-position display devices ofclaim 1 wherein the cathode drivers are also coupled to the dividerjunction so that the impedance of a portion of the divider will vary asan inverse function of the number of cathode elements that are beingdriven, to prevent spurious glow in the device irrespective of thedisplay pattern.

3. The apparatus for operating multiple-position display devices ofclaim 2 wherein the output circuits of the cathode drivers are eachcoupled to the divider junction by impedance means and appear inelectrical parallel with a portion of the divider when the cathodedrivers are activated.

4. The apparatus defined in claim 3 wherein the voltage dividing meanscomprises a resistive voltage divider and the cathode driver outputterminals are each coupled to the voltage divider junction by resistancemeans.

5. The apparatus for operating multiple-position display devices ofclaim 2 wherein the cathode drivers are each coupled in electricalparallel with a portion of the voltage dividing means.

6. The apparatus defined in claim 5 wherein the voltage dividing meanscomprises a resistive voltage divider and the cathode driver outputterminals are each coupled to the voltage divider junction by resistancemeans.

7. The apparatus for operating multiple-position display devices ofclaim 1 wherein the means for energizing the anodes includes a driverfor each of the anodes coupled for driving them responsive to the secondset of input signals and in synchronism with the first set of inputsignals applied to the cathode drivers.

8. The apparatus defined in claim 7 further comprising a voltagereference device connected in series with an impedance means between apair of reference terminals and the anodes each being coupled to thejunction of them by reverse-biased assymetrically conductive means.

9. A character display circuit comprising an envelope containing anionizable gas,

an anode and a plurality of cathodes within said envelope, each of saidcathodes having the shape of a segment of a character to be displayed,

circuit means for establishing a glow potential betwee h said anode anddifferent combinations of said cathodes to glow and thereby displaydifferent characters,

said circuit means including a plurality of cathode drivers, oneconnected to each of said cathodes, and means for selectively energizingsaid cathode drivers to render their connected cathodes glow ing,

an auxiliary electrode in contact with the ionizable gas and inoperative relation with said anode and cathodes, the current throughsaid auxiliary electrode being a function of the number of cathodeswhich are glowing, and bias circuit means for biasing said auxiliaryelectrode to a voltage intermediate the operating voltage of said anodeand said cathodes, said bias circuit means including at least oneimpedance device electrically connected to said auxiliary electrode,

said cathode drivers being connected electrically across at least aportion of said impedance device and serving to change the level of theimpedance connected to said auxiliary electrode as each cathode driveris energized.

lll. A character display circuit as in claim 9 wherein said currentpassesfrorn the anode through the ionizable gas to the auxiliaryelectrode, and at least a portion of said current flow passes throughsaid impedance device and tends to increase the voltage on the auxiliaryelectrode as the number of glowing cathodes increases, and

wherein the level of the impedance connected to the auxiliary electrodeis reduced as each additional cathode driver is energized, to compensatefor the tendency of the auxiliary electrode to increase in voltage asthe number of glowing cathodes increases.

11. A character display circuit as in claim 9 wherein the cathodedrivers are transistors, and

wherein the means for selectively energizing said cathode driverscomprises circuit means connected to the transistors to render them moreconductive in response to input signals, and

wherein the transistors are all connected across at least a portion ofthe impedance device to reduce the effective impedance connected to saidauxiliary electrode for each transistor that is energized.

12. A character display circuit as in claim 9 further including aplurality of additional impedance devices, one connected in series witheach of said current drivers and the series circuit is connected acrossat least a portion of the first-mentioned impedance device, and

wherein the current drivers are rendered conductive when energized, sothat as each driver is energized its associated additional impedancedevice is effectively connected across the first-mentioned impedancedevice.

13. A character display circuit as in claim 9 wherein the impedancedevice comprises a voltage divider having a junction connected to theauxiliary electrode, a predetermined impedance connected from saidjunction to a first reference potential terminal, and a secondpredetermined impedance connected from said junction to a secondreference potential terminal.

14. A character display circuit as in claim wherein each cathode driveris connected in series with an additional impedance driver, and eachsuch series is connected from said junction to one of said referencepotential terminals.

15. A circuit to compensate for voltage changes on an auxiliaryelectrode located in a gaseous atmosphere of a glow discharge indicatortube which has an anode and a plurality of cathodes in the gaseousatmosphere in operative relation to the auxiliary electrode, each of thecathodes being in the shape of a segment of a character to be displayedand being capable of exhibiting cathode glow when energized, comprisingcircuit means for energizing said anode and different combinations ofsaid cathodes to display different characters,

said circuit means including a plurality of cathode drivers, eachconnected to one of said cathodes and serving to energize the cathode tocause it to glow response to an input signal, and

bias circuit means for biasing said auxiiiary electrode to a voltageintermediate the operating voltage of said anode and said cathodes,

said bias circuit means including at least one impedance deviceconnected electrically to said auxiliary electrode, the current throughthe auxiliary electrode to said impedance device being a function of thenumber of cathodes which are glowing, and

said cathode drivers being connected electrically across at least aportion of said impedance device to modify the effective impedanceconnected to said auxiliary electrode as each of the cathode driversresponds to an input signal to cause its connected cathode to glow, soas to compensate at least in part for any voltage change which theincreased current through the auxiliary electrode tends to produce as anincreased number of cathodes glow.

16. A voltage compensation circuit as in claim wherein the impedancedevice comprises a voltage divider having a junction connected to theauxiliary electrode, a first predetermined impedance connected from saidjunction to a first reference potential terminal, and a secondpredetermined impedance connected from said junction to a secondreference potential terminal.

17. A voltage compensation circuit as in claim 16 further including aplurality of resistors, one connected in series with each of saidcathode drivers, and

wherein said cathode drivers are transistors, so that a plurality ofresistor-transistor series circuits are connected from said junction toone of said reference potential terminals, and

wherein as each transistor is energized it causes its connected cathodeto glow and its seriesconnected resistor to be effectively connectedacross one of said predetermined impedances.

18. A voltage compensation circuit as in claim 17 wherein said first andsecond predetermined impedances are first and second resistors.

19. A voltage compensation circuit as in claim 15 further including ananode voltage source terminal and circuit means for connecting saidterminal to said anode,

a cathode voltage source terminal, with the cathode drivers beingconnected between the respective cathodes and said cathode voltagesource terminal, and

wherein said impedance device comprises a voltage divider having ajunction connected to said auxiliary electrode, a first predeterminedimpedance connected from said junction to said anode voltage sourceterminal, and a second predetermined impedance connected from saidjunction to said cathode voltage source terminal.

20. A character display circuit for displaying any one ofa plurality ofcharacters in each of a plurality of sideby-side character positions,comprising a plurality of anodes, one in each of said characterpositions,

a piurality of groups of cathodes, each such group being associated withone of said character positions, each of the cathodes having the shapeof a segment of one of the characters to be displayed,

each of said anodes and its associated cathodes being disposed in anenvelope having an ionizahle gas atmosphere capable of sustainingcathode glow,

a plurality of cathode conductors each electrically connected to one ofthe cathodes in each character position,

a plurality of cathode drivers, each connected to one of said cathodeconductors, for energizing said cathodes selectively in response to afirst set of input signals,

circuit means for selectively energizing said anodes, in synchronismwith the selective energization of said cathodes, in response to asecond set of input signals, for displaying selected characters in eachof said character positions,

an auxiliary electrode in the gaseous atmosphere associated with eachcharacter position, the current flow therethrough being a function ofthe number of cathodes which are glowing, and

bias circuit means for maintaining an electrical potential within apredetermined range on said auxiliary electrode, irrespective of thenumber of cathodes glowing,

cathode driver energizes one of said cathodes. 21. A character displaycircuit as in claim 20 wherein the auxiliary electrode contains aportion extending between the anode and cathodes of each characterposition and those of the next adjacent character position, toelectrically isolate the electrodes of the respective characterpositions from each other.

1. Apparatus for operating multiple-position display devices having aplurality of interconnected groups of cathode elements, an anodeassociated with each of the groups and an auxiliary electrode that iscommon to all of the groups and shields them from each other comprisinga plurality of drivers having their output terminals coupled tocorresponding ones of the interconnected cathode elements for energizingthem selectively in response to a first set of input signals, voltagedividing means coupled between a pair of reference terminals and havinga divider junction, means coupled to each of the anodes for energizingthem selectively in response to a second set of input signals, and beingbiased in common with the voltage dividing means from one of saidreference terminals, the auxiliary electrode being coupled to thedivider junction to be biased at a level that is directly proportionalto the anode biasing potential for preventing spurious glow in thedevice irrespective of variations in the bias potential available forthe device.
 2. The apparatus for operating multiple-position displaydevices of claim 1 wherein the cathode drivers are also coupled to thedivider junction so that the impedance of a portion of the divider willvary as an inverse function of the number of cathode elements that arebeing driven, to prevent spurious glow in the device irrespective of thedisplay pattern.
 3. The apparatus for operating multiple-positiondisplay devices of claim 2 wherein the output circuits of the cathodedrivers are each coupled to the divider junction by impedance means andappear in electrical parallel with a portion of the divider when thecathode drivers are activated.
 4. The apparatus defined in claim 3wherein the voltage dividing means comprises a resistive voltage dividerand the cathode driver output terminals are each coupled to the voltagedivider junction by resistance means.
 5. The apparatus for operatingmultiple-position display devices of claim 2 wherein the cathode driversare each coupled in electrical parallel with a portion of the voltagedividing means.
 6. The apparatus defined in claim 5 wherein the voltagedividing means comprises a resistive voltage divider and the cathodedriver output terminals are each coupled to the voltage divider junctionby resistance means.
 7. The apparatus for operating multiple-positiondisplay devices of claim 1 wherein the means for energizing the anodesincludes a driver for each of the anodes coupled for driving themresponsive to the second set of input signals and in synchronism withthe first set of input signals applied to the cathode drivers.
 8. Theapparatus defined in claim 7 further comprising a voltage referencedevice connected in series with an impedance means between a pair ofreference terminals and the anodes each being coupled to the junction ofthem by reverse-biased assymetrically conductive means.
 9. A characterdisplay circuit comprising an envelope containing an ionizable gas, ananode and a plurality of cathodes within said envelope, each of saidcathodes having the shape of a segment of a character to be displayed,circuit means for establishing a glow potential between said anode anddifferent combinations of said cathodes to glow and thereby displaydifferent characters, said circuit means including a plurality ofcathode drivers, one connected to each of said cathodes, and means forselectively energizing said cathode drivers to renDer their connectedcathodes glowing, an auxiliary electrode in contact with the ionizablegas and in operative relation with said anode and cathodes, the currentthrough said auxiliary electrode being a function of the number ofcathodes which are glowing, and bias circuit means for biasing saidauxiliary electrode to a voltage intermediate the operating voltage ofsaid anode and said cathodes, said bias circuit means including at leastone impedance device electrically connected to said auxiliary electrode,said cathode drivers being connected electrically across at least aportion of said impedance device and serving to change the level of theimpedance connected to said auxiliary electrode as each cathode driveris energized.
 10. A character display circuit as in claim 9 wherein saidcurrent passes from the anode through the ionizable gas to the auxiliaryelectrode, and at least a portion of said current flow passes throughsaid impedance device and tends to increase the voltage on the auxiliaryelectrode as the number of glowing cathodes increases, and wherein thelevel of the impedance connected to the auxiliary electrode is reducedas each additional cathode driver is energized, to compensate for thetendency of the auxiliary electrode to increase in voltage as the numberof glowing cathodes increases.
 11. A character display circuit as inclaim 9 wherein the cathode drivers are transistors, and wherein themeans for selectively energizing said cathode drivers comprises circuitmeans connected to the transistors to render them more conductive inresponse to input signals, and wherein the transistors are all connectedacross at least a portion of the impedance device to reduce theeffective impedance connected to said auxiliary electrode for eachtransistor that is energized.
 12. A character display circuit as inclaim 9 further including a plurality of additional impedance devices,one connected in series with each of said current drivers and the seriescircuit is connected across at least a portion of the first-mentionedimpedance device, and wherein the current drivers are renderedconductive when energized, so that as each driver is energized itsassociated additional impedance device is effectively connected acrossthe first-mentioned impedance device.
 13. A character display circuit asin claim 9 wherein the impedance device comprises a voltage dividerhaving a junction connected to the auxiliary electrode, a predeterminedimpedance connected from said junction to a first reference potentialterminal, and a second predetermined impedance connected from saidjunction to a second reference potential terminal.
 14. A characterdisplay circuit as in claim 5 wherein each cathode driver is connectedin series with an additional impedance driver, and each such series isconnected from said junction to one of said reference potentialterminals.
 15. A circuit to compensate for voltage changes on anauxiliary electrode located in a gaseous atmosphere of a glow dischargeindicator tube which has an anode and a plurality of cathodes in thegaseous atmosphere in operative relation to the auxiliary electrode,each of the cathodes being in the shape of a segment of a character tobe displayed and being capable of exhibiting cathode glow whenenergized, comprising circuit means for energizing said anode anddifferent combinations of said cathodes to display different characters,said circuit means including a plurality of cathode drivers, eachconnected to one of said cathodes and serving to energize the cathode tocause it to glow in response to an input signal, and bias circuit meansfor biasing said auxiliary electrode to a voltage intermediate theoperating voltage of said anode and said cathodes, said bias circuitmeans including at least one impedance device connected electrically tosaid auxiliary electrode, the current through the auxiliary electrode tosaid impedance device being a function of the number of cathodes whichare glowing, and said cathode drivers being connected electricallyacross at least a portion of said impedance device to modify theeffective impedance connected to said auxiliary electrode as each of thecathode drivers responds to an input signal to cause its connectedcathode to glow, so as to compensate at least in part for any voltagechange which the increased current through the auxiliary electrode tendsto produce as an increased number of cathodes glow.
 16. A voltagecompensation circuit as in claim 15 wherein the impedance devicecomprises a voltage divider having a junction connected to the auxiliaryelectrode, a first predetermined impedance connected from said junctionto a first reference potential terminal, and a second predeterminedimpedance connected from said junction to a second reference potentialterminal.
 17. A voltage compensation circuit as in claim 16 furtherincluding a plurality of resistors, one connected in series with each ofsaid cathode drivers, and wherein said cathode drivers are transistors,so that a plurality of resistor-transistor series circuits are connectedfrom said junction to one of said reference potential terminals, andwherein as each transistor is energized it causes its connected cathodeto glow and its series-connected resistor to be effectively connectedacross one of said predetermined impedances.
 18. A voltage compensationcircuit as in claim 17 wherein said first and second predeterminedimpedances are first and second resistors.
 19. A voltage compensationcircuit as in claim 15 further including an anode voltage sourceterminal and circuit means for connecting said terminal to said anode, acathode voltage source terminal, with the cathode drivers beingconnected between the respective cathodes and said cathode voltagesource terminal, and wherein said impedance device comprises a voltagedivider having a junction connected to said auxiliary electrode, a firstpredetermined impedance connected from said junction to said anodevoltage source terminal, and a second predetermined impedance connectedfrom said junction to said cathode voltage source terminal.
 20. Acharacter display circuit for displaying any one of a plurality ofcharacters in each of a plurality of side-by-side character positions,comprising a plurality of anodes, one in each of said characterpositions, a plurality of groups of cathodes, each such group beingassociated with one of said character positions, each of the cathodeshaving the shape of a segment of one of the characters to be displayed,each of said anodes and its associated cathodes being disposed in anenvelope having an ionizable gas atmosphere capable of sustainingcathode glow, a plurality of cathode conductors each electricallyconnected to one of the cathodes in each character position, a pluralityof cathode drivers, each connected to one of said cathode conductors,for energizing said cathodes selectively in response to a first set ofinput signals, circuit means for selectively energizing said anodes, insynchronism with the selective energization of said cathodes, inresponse to a second set of input signals, for displaying selectedcharacters in each of said character positions, an auxiliary electrodein the gaseous atmosphere associated with each character position, thecurrent flow therethrough being a function of the number of cathodeswhich are glowing, and bias circuit means for maintaining an electricalpotential within a predetermined range on said auxiliary electrode,irrespective of the number of cathodes glowing, said bias circuit meansincluding at least one impedance device in series with said auxiliaryelectrode, a plurality of resistors, each of which is connected to oneof said cathode drivers, and circuit means connecting each said cathodedriver and connected resistor across at least a portion of saidimpedance device, so as to reduce the effective impedance coNnected tosaid auxiliary electrode as each such cathode driver energizes one ofsaid cathodes.
 21. A character display circuit as in claim 20 whereinthe auxiliary electrode contains a portion extending between the anodeand cathodes of each character position and those of the next adjacentcharacter position, to electrically isolate the electrodes of therespective character positions from each other.